PRELIMINARY
CYW54907
a. (Crystal) Use WRF_XTAL_XON and WRF_XTAL_XOP.
b. See “External Frequency Reference” for alternative connection methods.
c. It is the responsibility of the equipment designer to select oscillator components that comply with these specifications.
d. Assumes that external clock has a flat phase noise response above 100 kHz.
3.3 External 32.768 kHz Low-Power Oscillator
The CYW54907 uses a secondary low frequency clock for low-power-mode timing. Either the internal low-precision LPO or an
external 32.768 kHz precision oscillator is required. The internal LPO frequency range is approximately 33 kHz ± 30% over process,
voltage, and temperature, which is adequate for some applications. However, one tradeoff caused by this wide LPO tolerance is a
small current consumption increase during power save mode that is incurred by the need to wake-up earlier to avoid missing beacons.
Whenever possible, the preferred approach is to use a precision external 32.768 kHz clock that meets the requirements listed in
Table 4.
Table 4. External 32.768 kHz Sleep Clock Specifications
Parameter
LPO Clock
Units
kHz
ppm
%
Nominal input frequency
Frequency accuracy
Duty cycle
32.768
±200
30–70
Input signal amplitude
Signal type
200–3300
mV, p-p
–
Square-wave or sine-wave
Input impedancea
>100k
<5
Ω
pF
Clock jitter (during initial start-up)
<10,000
ppm
a. When power is applied or switched off.
Document Number: 002-19312 Rev. *C
Page 14 of 95
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